We can gain insight into the dominant low-\(T\)  scattering mechanism in graphene by comparing \(\sigma (n)\)  before and after current annealing. The linearity of \(\sigma (n)\)  before annealing suggests the dominance of charged impurity scattering [1]}, [2]}, [3]}. For screened Coulomb potential scattering, the scattering time is \(\tau \propto k_F\)  [2]}, [5]} which leads to a conductivity \(\sigma =\frac{2e^2}{h}k_F v_F \tau \propto n\) , with \(k_F\)  being the Fermi wavevector. The mean free path in these devices is \(l_m = \sigma h/2e^2 k_F \sim 150\)  nm, much smaller than the sample size (\(> 1~\mu \) m), justifying the use of the Boltzmann model for unannealed devices.
